The present invention is related generally to electrical communication systems and more specifically to automatic communication systems for monitoring the presence of individual at predetermined locations.
It is desireable in numerous situations to monitor the location of employees or other individuals. For example, in U.S. Pat. No. 4,495,496, a Personnel Monitoring And Locating System is disclosed for use in underground mines. A plurality of remote terminals having transceivers are positioned throughout the mine. Periodically, the remote terminals are activated to transmit interrogation signals. Each miner to be monitored is equipped with a transponder that replies to the interrogation signal with a reply signal. The reply signals are time-delayed by a predetermined amount of time that is different for each of the transponders so that the reply from each transponder is time-spaced with respect to the replies from the other transponders. A host computer at the surface is linked to each remote terminal for activating the remote terminals to transmit the interrogation signals and for receiving the reply signals from the remote terminals which are indicative of the location of each transponder equipped miner.
Another monitoring apparatus is disclosed in U.S. Pat. No. 4,338,601. In that patent, a system is disclosed wherein a watchman carries a portable memory module which he couples to various different stations as he makes his rounds. Each station includes a particular configuration of permanent magnets which provides that station with its own predetermined magnetic code. The portable memory module stores the code of each station as it is visited by the watchman. By reading the information stored in the portable memory module, each station which the watchman visited and the order in which he visited the stations can be determined.
In other situations, it is desireable to monitor individuals other than employees. For example, in U.S. Pat. No. 4,011,409, a system is disclosed in which old or sick persons call a predetermined number at regular intervals. Their calls light an indicator light which informs an attendant that they are allright and have called in. Individuals who have not called in may be called or visited by appropriate personnel.
Over the last several years, with the overcrowding of jails and work-release centers and the increased costs of keeping an individual incarcerated, the application of such techniques to the electronic supervision of criminals has gained increased attention. Benefits, such as relieving overcrowded jails, preventing the incarceration of non-violent criminals or persons guilty of less serious crimes with career criminals, and allowing probation or parole officers to keep track of a substantially larger number of parolees than in the past, have caused greater attention to be focused upon the possibilities of automatic electronic monitoring of parolees. Prior art personnel monitoring systems, however, are not effective for monitoring parolees. Systems such as those disclosed in the '496 patent, which would automatically respond without requiring the parolee to take any action, or the '409 patent, wherein the parolee would merely call a central location from any location having a phone, cannot be used to determine if a parolee is at a given location during a predetermined time period. A system such as that disclosed in the '601 patent would require the parolee to carry a memory module which could be lost, damaged, or tampered with. None of these systems provides the security, reliability, and effectiveness required of a parolee monitoring system.
The designers of parolee monitoring systems are faced with a large number of competing design criteria. First, if the system is used in conjunction with a home telephone of the parolee, the system must not interfere with the normal operation of the telephone. Secondly, the system should be capable of interfacing with the telephone through a minimal number of connections. The system must be simple to operate, effective, and tamper proof to prevent the parolee from defeating the system. In many instances, such design criteria require numerous trade-offs from an engineering standpoint.
It is known to locate equipment in the homes of individuals for the gathering of specific information. Such equipment often uses ordinary telephone lines to transmit the gathered information to another location. For example, in U.S. Pat. No. 4,082,921, a computer at a central office is connected to an automatic answering system at the subscriber's home either with or without ringing the subscriber's telephone. Tones sent by the computer to the automatic answering system are filtered and compared to a reference signal. A connect signal is furnished when the comparator indicates that the tones signifying that particular billing system have been received. The connect signal energizes a relay which connects the billing system to the telephone system. Although such a system can be effected by ringing the subscriber's telephone, it is common to make the connection with the subscriber's billing system without ringing the subscriber's telephone. In this manner, the billing information can be obtained without disturbing the subscriber.
U.S. Pat. No. 4,332,980 discloses a system utilizing transmissions which are transparent to normal telephone service for gathering information regarding alarm surveillance, meter reading, energy management and digital data service. This information is gathered without disturbing the subscriber.
In U.S. Pat. No. 3,483,327, a radio transmitter at the subscriber's home transmits viewing information to a transponder/receiver also located at the subscriber's home. The transponder/receiver s interrogated via telephone lines to obtain the viewing information. This interrogation is performed without disturbing and without the knowledge of the participating subscriber.
Finally, in U.S. Pat. No. 4,126,762, an automatic dialer is used to call a remote station. If the automatic dialer sends appropriate ring signals, the remote station automatically connects a billing processor at the remote station to a data accumulator to thereby provide billing information. The remote station is designed to seize the telephone line and to prevent the telephone from responding with an audible call signal.
Although systems are known wherein equipment is provided at a subscriber location for obtaining desired information, such systems are typically designed to operate without any input from the subscriber, and often times with the subscriber totally unaware that the information is being gathered. Such systems are inapposite to monitoring systems wherein it is necessary for the parolee or other individual being monitored to appropriately respond and thereby confirm his presence at a predetermined location.